Strain rate has been reported to have a significant influence on the modulus and the tenacity of single fibers and yarns. Most of the experimental work on the properties of single fiber or bundle strength of cotton fibers is carried out on extremely low strain rates (=8% per min). The strength values obtained in this manner have shown very good correlation with yarn strength determined at approximately the same strain rate. However, in recent years the yarns are being subjected to extremely high cyclic rates of extension (cyclic rates 600 cycles/min. at 400-800% per min.), during weaving on air-jet and projectile looms, which makes the correlation difficult, if not irrelevant. Moreover the fiber testing is also being carried out at much higher rates of extension on high speed instruments such as HVI as compared to much slower rates on Pressley or Stellometer. Studies on the effect of strain rate on the strength of single fibers, yarns and yarns with varying short fiber percentages is reported.